It is generally old, as shown in U.S. Pat. No. 3,893,717, to support an inner casing in a well of an outer casing by means of a resiliently expandable and contractible locking ring. The present device is directed to an improved releasable holding means for initially preventing the locking ring from moving axially on the casing hanger until the locking ring expands and engages into a locking notch on the second member and thereafter provides a forced expansion of the locking ring into engagement in the locking notch.